A variety of refrigerant compressors for use in vehicle air conditioning systems are currently available. Two of the more popular vehicle compressor designs are the variable capacity axial type and the radial type, both of which use a series of pistons operating in an array of cylinders to compress the refrigerant gas.
In a wobble plate axial type compressor, the cylinders are equally, angularly spaced about and equally radially spaced from the axis of a central drive shaft. A piston is mounted for reciprocal sliding motion in each of the cylinders. Each piston is connected to a non-rotary swash plate or wobble plate received about and operatively connected to the drive shaft through a rotary drive plate.
During operation of the compressor, rotation of the drive shaft and drive plate imparts a wave-like reciprocating motion to the wobble plate. This driving of the wobble plate in a nutating path serves to impart a linear reciprocating motion to the pistons. By varying the angle of the wobble plate and drive plate relative to the drive shaft, the displacement or capacity of the compressor may be varied to effect the desired level of compressing action. The discharge from the cylinders is mixed in a discharge chamber in the housing, and to some extent pressure/sound energy pulsations are attenuated by the mixing action. An axial compressor of this type is disclosed in, for example, U.S. Pat. No. 4,428,718 to Skinner, entitled "Variable Displacement Compressor Control Valve Arrangement", issued Jan. 31, 1984, and assigned to the assignee of the present invention.
In a radial type compressor, a cylinder block is provided having an array of radially arranged cylinders. Each cylinder defines a piston receiving bore that is closed by a discharge valve assembly. A piston is positioned for reciprocation in each bore and driven by a crank shaft operatively connected to the engine of the vehicle. This compressor includes an annular discharge chamber defined between the periphery of the cylinder block and an outer cylindrical shell, which also tends to smooth out the inherent pulsations.
The radial type compressor is relatively compact and lightweight when compared to the wobble plate axial type compressor. This is because the radially extending pistons allow the compressor to be made with a minimal axial length. Accordingly, the compressor housing may be both smaller in size and lighter in weight. This makes the radial compressor particularly suited for utilization in compact vehicles. A radial compressor of the type described is disclosed in, for example, U.S. patent application Ser. No. 07/751,370 filed Aug. 28, 1991, entitled "Radial Compressor with Discharge Chamber Dams" and assigned to the assignee of the present invention.
While these piston type compressors provide a very effective way to compress and circulate the refrigerant fluid in a vehicle air conditioning system, an adverse side effect concerns delivery of the compressed gas in high pressure and noisy pulsations coincident with the discharge strokes of the pistons, rather than in a reasonably constant pressure and quiet condition. This shortcoming has to some extent been alleviated by the mixing chamber concept, but it has not been entirely solved. In addition to creating a rougher and noisier operating system, these discharge energy pulsations tend to lead to premature fatigue and failure of component parts throughout the air conditioning system, thereby diminishing its reliability.
Various attempts, other than providing mixing chambers, have been made to further reduce the effect of these energy pulsations in order to provide the desired smoother, quieter and more reliable compressor. One of the more successful approaches to date is disclosed in pending U.S. patent application Ser. No. 07/787,180 filed Nov. 4, 1991, entitled "Variable Discharge Flow Attenuation for Compressor" and assigned to the assignee of the present invention. In this approach, a rotary valve is positioned adjacent the discharge port of the discharge chamber in a wobble plate axial type compressor. This valve alternately covers and uncovers the discharge port of the compressor. The spaced variable flow orifices of the valve serve to attenuate the pulsations that occur during the operating cycle. Each flow orifice is preferably pear-shaped, and positioned with the necessary circumferential spacing for synchronization with the pumping stroke of the pistons within the compressor cylinders.
While the disclosed rotary valve is particularly effective in further attenuating pressure pulsations and thereby smoothing the operation and extending the service life of the compressor, this approach has a shortcoming. It is only readily integratable into a compressor of the axial type. Relatively extensive modifications are needed in a compressor of radial design in order to effectively utilize this concept.
Additionally, it must be noted that the already oversized axial-type compressor must actually be further enlarged to accommodate the rotary valve and the special nozzles that form the porting required. Accordingly, space limitations in a vehicle could even prevent the incorporation of an axial-type compressor modified to include this attenuator. Further, it should be noted that the rotary valve concept is not able to be easily retrofitted to previously designed and manufactured compressors. Similarly, the spaced dam attenuation concept in the discharge chamber of a radial compressor, described and claimed in the prior application Ser. No. 07/751,370 referenced above, is generally limited to incorporation in new radial compressors. Also, sound energy attenuation is limited since metal components are required. In view of this, it should be appreciated that a need exists for an alternative approach to provide attenuation of pressure/ sound energy pulses of the refrigerant gas being discharged from the compressor of a vehicle air conditioning system.